Morphology of printed lines and droplet deposits using hydrophilic nanoparticle suspensions

By Jim LyonREU Advisor Professor Megaridis

BackgroundPrinted lines containing micro-particles are used in development of printed wiring boards (PWB)The morphology of the printed lines would have an effect on the bulk electrical properties of the printed lineThese lines containing nanoparticle suspensions can be fabricated at a lower cost than commonly used lithographic techniques Example of complex conductive

patterns printed using a gold nanoparticle suspension the line widths are on the order of 100 microns1

1) Szczech, J.B., et al, Electronics Packaging Manufacturing, IEEE Transactions on , vol.25, no.1, pp.26-33, Jan 2002

Goals

Learn how to use the experimental setupPrint model nanoparticle suspensions and investigate the morphology of printed lines and dropletsDetermine the effect of geometry on the morphology of deposits

Image of a printed line of a

hydrophilic nanoparticle suspension

Generic PolymerPolybead® Carboxylate nanoparticle suspensions are chosen as generic hydrophilic polymer nanoparticle suspensionsThe suspension consisted of spherical nanoparticles with a nominal particle diameter of 0.0458 μConcentration of the polymer was 2.65% by weight with the remaining suspension being composed of an unknown combination of water and surfactant

Droplet Experimental Setup

A syringe pump is used to control the flow of nanoparticle suspension through a needle tip (~100μ inner diameter)When a desired amount of liquid is at the tip of the needle the needle is lowered until it contacts the substrate depositing a dropletThe deposit on the substrate is then taken to an optical microscope for morphological study

Schematic of experimental setup used to create droplets

Droplets of Suspension

To determine the effect of geometry, on the morphology of deposits, droplets were createdPrevious papers have described a “coffee stain” effect in droplets of colloidal fluidsDetermine if this “coffee stain” will effect the morphology of our suspension

Dynamics of the “coffee stain” effect. The evaporation rate J is larger at the edge of a droplet due to the curvature of the droplet leading to a flow of fluid and nanoparticles with a velocity v.

Deegan, R.D., et al, “Capillary Flow as the Cause of Ring Stains from Dried Liquid Drops” , Nature 389, 1997

Droplets

Smaller droplets display a noticeable “coffee stain” effect with no visible cracks at the center of the line

Droplets, ctd.

Larger droplets display a “coffee stain” effect, however the larger droplet also contain cracks that go throughout the entire droplet

How to Effect the Morphology of dropletsA cap, with a hole cut into the center, is placed on top of a dropletThis will saturate the air

and alter the way a droplet placed beneath it evaporatesTwo methods were used to place droplets beneath the cap

Method one involved the lowering of the needle through the opening until it contacts the substrateMethod two involved placing the cap on top of an existing droplet

Drawing of the cap used to effect the morphology of droplet deposits

The cap alters the evaporation rate across the entire droplet by saturating the air the droplet is exposed toThrough adjusting the position of the opening of the cap, relative to the droplet, altered deposit morphologies are formed

Morphology of this droplet can then be examinedThis can be compared to droplets formed with out a cap

Expected evaporation pattern of droplet under a cap

How the Cap Works

Results from Cap Experiments

Method one: A droplet placed directly beneath the opening of a cap does not display cracks throughout the entire droplet

Method two: A droplet not placed directly beneath the opening of a cap displays an altered crack morphology around the edge of the droplet

Droplet ResultsThe morphology of droplets are dependent on the size of the droplet Droplets were observed to have a “coffee stain”effect

This “coffee stain” effect results in an increase in the concentration of the particles at the edge of the depositThis effect was more noticeable on droplets with a diameter of less than 1 mm

Estimates of the volume of these droplets are unreliableDeposits morphology is dependent on the evaporation rate across the droplet

Cap experiments show that altering the evaporation rate effects the morphologyTwo types of morphology are observed depending on how the droplet is placed beneath the cap

Printed Lines Experimental Setup

A syringe pump is used to control the flow of nanoparticle suspension through a needle tip (~100μ inner diameter)The suspension forms a liquid capillary-bridge between the needle and a moveable substrate located underneath and mounted on a motorized platform The printed line on the substrate is then taken to an optical microscope for morphological study

Schematic of experimental setup used to create printed lines

Line Printing of SuspensionDetermine the morphology of printed linesDetermine if printed lines will exhibit a morphology similar to dropletsDetermine if there is “coffee stain”effecting the edges of the printed lines

Image of a printed line of a

hydrophilic nanoparticle suspension

Estimating Layers of Nanoparticle

16.715855440.04580.7655860.19231

9.8967333760.04580.453270.16240.5

7.6962306480.04580.3524870.12530.3

2.9037570010.04580.1329920.11070.1

Averaged Layers of Particles

Diameter of Particle (micron)

Height of line (micron)

Width of Line (cm)

Flow Rate (ml/hr)

Q ConcentrationHWidth Velocity×

=×

HLayers of ParticlesD

=

Printed Lines

~3 layers no crack development ~8 layers crack development

~17 layers crack development~10 layers crack development

Printed Line resultsCracking develops when the average number of nanoparticle layers is greater than 8 layersCracking develops all the way through a line when the average number of nanoparticle layers is larger than 17Cracking is more prominent at the edges and the center of printed lines

Why Prominent Cracks Develop in the CenterThe contact line must remain pinnedObservations of printed lines showed that lines were pinned initially for a period of timeThe contact line then becomes unpinned and begins to recede toward the center of the lineThe receding contact line carries nanoparticles and deposits them in the center creating more layers of nanoparticles in the center

Images of a receding contact line developing cracks at the edges and at the center of the line

Nanoparticle Layers Needed for Cracks to Form

Cracks develop at the edges when the average number of layers is ~8Cracks develop throughout the entire width of the deposit when the average number of layers is ~17Because of processes effecting the number of layers present in different areas of the line the number of layers needed to develop cracking is found to be between 8 and 17 layers

~8 layers crack development

~17 layers crack development

Areas for Future Study

Altering the morphology of printed linesUse the understanding gained here to print conductive lines with controlled morphologyPrinting a polymer solution using the novel printing technique of creating a capillary-bridge

Acknowledgements

National Science FoundationDepartment of DefenseManish TiwariProfessor YarinProfessor TakoudisProfessor Jursich

References[1] Szczech, J.B.; Megaridis, C.M.; Gamota, D.R.; Jie Zhang, "Fine-line conductor manufacturing using drop-on demand PZT printing technology," Electronics Packaging Manufacturing, IEEE Transactions on , vol.25, 2002[2] Kim, Dongjo; Jeong, Sunho; Park, B.K.; Moon, Jooho, “Direct writing of silver conductive patterns: Improvement of film morphology and conductance by controlling solvent compositions,” Applied Physics Letter, vol. 89, 2006[3] Deegan, R.D.; Bakajin , O.; Dupont, T.F.; Huber, G.; Nagel S.R.; Witten T.A., “Capillary flow as the cause of ring stains from dried liquid drops.”. Nature, vol. 389, 1997[4] Deegan, R.D.; Bakajin , O.; Dupont, T.F.; Huber, G.; Nagel S.R.; Witten T.A., “Contact line deposits in an evaporating drop.”. Physics Review E, vol. 62, 2000[5] Parashkov, R.; Becker, E.; Riedl, T.; Johannes, H.H.; Kowalsky, W., "Large Area Electronics Using Printing Methods," Proceedings of the IEEE , vol.93, 2005[6] Gratson, G.M.; Xu, M.; Lewis, J.A., “Microperiodic structures: Direct writing of thee-dimensional webs,” Nature, vol. 428, 2004